Ribosome metabolism was studied in oocytes of Xenopus laevis. Treatment of folliculated oocytes with HCG in vitro caused an alteration in rate of ribosomal proteins synthesis and rate of ribosome assembly. Intermediates in the ribosome assembly process have been isolated and their characterization has been initiated. The hormone appears to have its affect on the final steps in the ribosome assembly process. Attempts at finding polycistronic polypeptide precursors to ribosomal proteins was a failure. It appears that all ribosomal proteins are individually ssnthesized on their own messenger RNAs. Ribosome metabolism was also studied in Tetrahymena pyriformis. By appropriately manipulating these cells theycan be induced to produce 40% of their protein as ribosomal structural protein. Polysomes isolated from those cells direct the synthesis of ribosomal proteins in vitro. Ribosomal protein synthesis is independently regulated relative to ribosomal RNA synthesis in these cells. BIBLIOGRAPHIC REFERENCES: R.L. Hallberg & D.C. Smith, 1975. Ribosomal protein synthesis in Xenopus laevis oocytes. Dev. Biol. 42: 40-52.